The invention relates to a path controller for vehicles whose path is influenced by cross currents in the medium in which the vehicle is traveling. Thus if the vehicle is airborne the travel path is affected by air currents whereas if the vehicle is a water craft it will be influenced by water currents.
The invention also relates to a path control system and a method for performing path control.
The invention is intended in particular for parachutes, balloons, aircraft and ships having manual or automatic steering.
Path controllers are known which are based on measurement of the orientation of the vehicle relative to the moving current influencing its path. The so-called azimuth angle xcex8 relative to the moving current is used for this purpose. The azimuth angle xcex8 represents the angle between the airspeed or velocity vector of the vehicle relative to air in the case of aircraft or relative to water in the case of water craft, and a given reference direction. This leads to a linear controller design. The necessary measurement of the actual azimuth angle xcex8, however, has disadvantages. It is extremely expensive to perform this measurement with gyroscopic systems, while compass systems are of only limited use when metal-containing cargo is to be transported. Moreover, because the wind conditions are known only imprecisely, the set azimuth angle xcex8 can be determined only imprecisely from the set path azimuth angle "khgr"s which is normally given.
German Patent application DE 43 36 056 A1 discloses a flight-control device for steering a parachute using a position-measuring unit comprising a GPS position sensor to calculate position data during flight, a steering unit and a servo unit connected therewith. Before the flight, a set path is introduced into the steering unit by a programming device. During the flight, the GPS positioning sensor continuously delivers the current position data of the parachute to the steering unit, in which these data are compared with the set flight-path data. In the event of a deviation of the actual position from the set position, the servo unit is actuated to bring the parachute back to the set flight path.
German Patent Application DE 196 25 561 A1 discloses a method for course control of waterborne vehicles, wherein position data of the ship are compared with a defined ground course line and from this there is computed deviation of the ship""s position relative to the defined ground course line. An autopilot adjusts the actual course of the ship appropriately, thus directing the ship toward and enabling it to reach the defined ground course line, and hold the ship on the defined course line.
German Patent Application DE 41 10 249 A1 regarded as the closest prior art to the present invention, discloses a path controller for ships with a cascade controller which is supplied with the distance of the ship from a set path, the course angle and the course angular velocity of the ship. For this purpose, the position of the ship can be determined by means of a satellite navigation system. In order to compensate for wind perturbations, the instantaneous yaw angle of the ship is minimized by a particular method for determining the gain factor of the course controller.
An object of the invention is to provide a path controller and path control system for vehicles having manual or automatic steering whose path is influenced by a moving current, as well as to provide a method for calculating a steering variable for such applications, which method is provided with a steering function by which the vehicle can be guided relative to a set path in a manner which is resistant with respect to external influences.
In accordance with the invention, path control is achieved on the basis of the angle difference between the actual path azimuth angle "khgr" and the set path azimuth angle "khgr"S represented as the angle between navigation velocity, i.e. the ground speed vector, and a given reference direction.
In particular, the value of the control signal v for the vehicle is expressed as a curve with respect to the angle difference.
Specifically, the curve of the value of v with respect to xcex94"khgr" and has a negative slope when xcex94"khgr"=0 and the curve changes sign at each interval when xcex94"khgr"=xcfx80 while keeping the same sign in each interval.